Trunked RF communication systems are known in the art. In general, such systems typically include a plurality of communication resources (such as single or paired frequencies, which frequencies may or may not support TDM time slots) that are supported by a like number of repeaters. The allocation of these resources amongst various communication units (such as portable units, mobile units, and fixed location units) is directed by a resource controller (which may be centrally situated, or distributed, such as, for example, within the repeater structure itself).
Some systems support a plurality of communication capabilities. For example, while some or all of the communication resources will typically support dispatch service, at least some of the resources may also support telephone interconnect services, secure (encrypted) services, paging services, data services, and other extended capability services. Generally, when initiating a communication, a communication unit will provide some sort of indication, such as an op-code, to the resource controller to indicate the type of service requested. The resource controller then functions, at least in part, to ensure that the communication unit has access to a resource having the necessary capability or capabilities.
Prior art systems do not necessarily allocate such multi-capability resources in an efficient manner. For example, a communication resource that will support both secure and interconnect services may be assigned to a communication unit that only requires interconnect service, notwithstanding the possible availability of another resource that might support telephone interconnect service but not secure communications. By allowing the above allocation, the resource controller causes usurpation of the secure capability, since that capability is no longer available to other users for the duration of that particular communication.
Another problem exists in that prior art trunked systems tend to maintain all communication resources as available to all communication units, provided only that a requesting communication unit be capable of exercising one or more of the communication capabilities of a candidate resource. Therefore, some communication users, such as public safety agencies, are often required to own, maintain, and operate a privately owned trunked radio system in order to ensure that communication facilities are available when needed. Such agencies are precluded from considering the option of purchasing air time from a third party provider of communication resources, such as a SMR (specialized mobile radio) service.